The manifest and the resource
When you add a manifest you need to make sure that you give it the right resource type. If for some reason your manifest is not being picked up and you've ruled out fusion caching, then make sure that you don't have this:
The first resource 1033 will not get picked up because of the "101". It should be under 24 and then 1.
You can get Resource Hacker here. You can do the same with Visual Studio of course.